Messages in this thread | | | Date | Tue, 17 Apr 2012 18:29:42 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v4 2/3] genirq: reimplement exit_irq_thread() hook via task_work_add() |
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On 04/17, David Howells wrote: > > Oleg Nesterov <oleg@redhat.com> wrote: > > > 2. change irq_thread() to do task_queue_work(irq_thread_dtor) > > at the start and task_work_cancel() before return. > > > > tracehook_notify_resume() can never play with kthreads, > > only do_exit()->exit_task_work() can call the callback > > and this is what we want. > > Hmmm... This seems wrong.
I don't agree...
> You're now using the hook in two distinct ways: > the primary use of that the hook is to detect that userspace is about to > resume processing (via TIF_NOTIFY_RESUME)
Yes,
> and then you're abusing the fact > that the hook is also invoked via do_exit() to perform a clean up because > we've got to get rid of it somehow under that circumstance.
Yes, and please note that this cleanup is only needed if irq thread crashes.
> This only works for you because you're operating in a kernel thread which > doesn't have a userspace (and so will never see TIF_NOTIFY_RESUME).
Yes,
> However, > if someone tries that in an ordinary thread,
Sure, nobody should do this with the ordinary thread. At least exactly this.
> it is liable to malfunction as > the record could be executed and deleted at some unpredictable point in the > future.
"In the future" is not possible (and this doesn't depend on PF_KTHREAD). irq_thread() does task_work_cancel() before return. And until it returns it returns the work can't be executed unless this task exits in between.
Oleg.
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